Recently, in the field of image capturing equipment, digital camcorders and digital still cameras have had their image quality and their versatile shooting capabilities tremendously improved by leaps and bounds. Examples of major indices to the image quality of a moving picture that can be shot by these image capture devices include the number of pixels per frame (representing a resolution), the number of frames per second (what is called a “frame rate”) and the ratio of image signal to noise (i.e., the signal to noise ratio (SNR)).
Various levels of resolutions are now available and one of them can be used adaptively according to the image quality to be achieved by a given image capture device. For instance, although the resolution of a TV phone is represented by the number of pixels that is roughly as large as what is required by QCIF (Quarter Common Intermediate Format), digital single-lens reflex cameras nowadays have a resolution exceeding 10 megapixels. Likewise, there is a broad range of frame rates available. For example, digital still cameras now achieve a frame rate of several frames per second in the sequential shooting mode, camcorders now have a frame rate of 30 frames per second, and a special-purpose high speed shooting camera could achieve even a frame rate exceeding 1,000 frames per second.
However, it is difficult for imagers (such as CCDs and CMOS image sensors), which are currently used extensively in those image capture devices, to increase pixel data reading rate endlessly. That is to say, the pixel data reading rate should have a certain upper limit. And the upper limit of the pixel data reading rate defines that of the product of a moving picture's resolution and the frame rate. That is why it has been hard for a conventional image capture device to shoot a moving picture so as to achieve both a high resolution and a high frame rate at the same time.
Thus, to overcome such a problem, many techniques have been proposed for generating a moving picture with a high resolution and a high frame rate by subjecting the moving picture to signal processing. For example, according to Patent Document No. 1, two moving pictures with mutually different combinations of resolution and frame rate are shot with two imaging means and then subjected to signal processing, thereby generating a moving picture with a high resolution and a high frame rate.
FIG. 20 illustrates a configuration for a conventional image capture device disclosed in Patent Document No. 1. In this image capture device, a part of the light that has been transmitted through a lens 1001 is further transmitted through a half mirror 1004 and then incident on a film 1002 by way of a shutter 1006. As a result, a moving picture with a high resolution but a low frame rate (i.e., the interval of shooting) is recorded (or shot) on the film 1002. On the other hand, another part of the light that has been transmitted through the lens 1001 is reflected by the half mirror 1004, passed through a lens 1005 and then received by a CCD 1005. Consequently, a moving picture with a low resolution but a high frame rate is shot and written on a storage medium (not shown).
The image capture device determines the correspondence between the image that has been recorded on the film 1002 and the image that has been shot with the CCD 1005 by comparing their edges to each other and generates, based on that correspondence, an image at a timing when an image was certainly shot with the CCD 1005 but was not shot with the film 1002. In this manner, the image capture device can generate an image that has both a high resolution and a high frame rate alike.
A conventional image capture device that uses such two imaging means records a moving picture with a high resolution but at a low frame rate using one of the two imaging means (i.e., the film 1002) and shoots and stores a moving picture with a low resolution but at a high frame rate using the other imaging means (i.e., the CCD 1003). That is why even if two imagers, of which the read rates have an upper limit, are used, a moving picture with a high resolution and a high frame rate, each of which is greater than the sum of the respective upper limits of those two imaging means, can still be generated.
Generally speaking, when a given image has a higher resolution than others, it means that the image has higher spatial frequency components than the other images that have been shot in the same range. Also, “to raise the resolution of a given image” means processing the image so that the processed image has higher spatial frequency components. Strictly speaking, even if a given image has a high resolution (i.e., high spatial frequency components), it does not always mean that the image has a great number of pixels. In other words, an image with a great number of pixels can have, but does not always have, high spatial frequency components. That is why to be an image with a great number of pixels is not synonymous to being an image with a high resolution. Nevertheless, for the sake of simplicity, an image with a great number of pixels is supposed to have a high resolution unless stated otherwise.
Patent Document No. 1: Japanese Patent Publication No. 3531035